EVOH resin has a high crystallinity based on hydrogen bonds between hydroxyl groups in side chain thereof, and additionally has a strong intermolecular force in amorphous portion thereof. These provide EVOH resin film with excellent gas-barrier property,
For the purpose of utilizing the excellent gas-barrier property, EVOH resin is molded into film, sheet or a container such as bottle used for packaging food, pharmaceutical, industrial medicine, agricultural chemicals, and so on. A typical form of EVOH resin to be distributed as a molding material is in the form of pellet.
EVOH resin pellet is classified into a cylindrical pellet produced by strand pelletizing process disclosed in, for example, JP H3-61507A (patent document 1), and a spherical pellet produced by hot-cut pelletizing process such as underwater pelletizing and midair hot-cut pelletizing disclosed in JP2001-96530A (patent document 2).
EVOH resin pellet, in either shape of cylinder or sphere, is produced by cutting water-containing or molten EVOH resin strand at every given length, and rinsing the resulting cut pieces (i.e. pellets), followed by drying.
Drying pellets is performed with hot-air flow dryer system or the like, from the viewpoint of improvement of drying efficiency or preventing pellets fusion. In the case that pellets are forced to be flown, the pellets are rubbed each other, and therefore burr or edge of the pellet, which is generated in pelletizing process, is broken to convert into fine particles or powders.
For these reasons, EVOH resin pellets contaminated with the rubbishes or powder generated. in production of the pellets may be distributed and supplied as a molding material. Such contaminated EVOH resin pellets cause quality of a resulting molded article impaired. For example, JP2005-36115A (patent document 3) discloses problematic issues of prior art: feeding to an extruder is likely unstable, and when a multilayer film is produced by melt-extrusion, surface boundary between EVOH resin layer and its adjacent layer may become turbulent to generate gel or the like.
The patent document 3 suggests methods for providing EVOH resin pellets free from the powder. The methods include removing powder with sieve, classification with cyclone separator, cleaning up powder by rinsing with solvent and drying, or fusing powder by drying at relatively high temperature after water-spraying, thereby discreating the powder.
Various apparatuses for removing powder or rubbishes, such as sieve type separators, cyclone separators, and electrostatic removers are suggested.